1. Field of the Invention
The present invention relates to an acceleration/deceleration control apparatus using a slip speed, and more particularly to an acceleration/deceleration control apparatus using a slip speed, for use in an induction motor to limit any excessively abrupt acceleration/deceleration of the induction motor.
2. Description of the Prior-art
Heretofore, the induction motor (will be referred to as "IM" hereinafter) has been widely utilized as a constant-speed motor with a power source of a predetermined frequency since it is sturdy and not expensive.
However, such IM has not been used as a servo motor for which a rapid acceleration/deceleration is required.
Recently, however, vector control of the IM has been industrially implemented, while the IM itself has been improved. Thus, the IM has a possibility of use as a servo motor. That is to say, since a power source of widely variable frequency has become available for driving the IM as a result of the recent technological innovation in the fields of the electronic devices, microcomputers, and software, the IM is being changed from the constant-speed motor to a servo motor.
Conventional vector control of slip frequency type will be explained herebelow with reference to FIG. 11.
FIG. 11 shows a basic concept of the slip-frequency type vector controller which comprises a speed control amplifier 101 to amplify the difference between a command speed .omega.r* and actual speed .omega.r, a divider 102, a constantsetter 103, a vector analyzer 104 to synthesize a torque current component and exciting current component, a adder 105 to synthesize a vector based on the output of a vector generator which will be described later and the output from the vector analyzer, a converter 106 to convert the adder output into a three-phase current signal, a current control amplifier 107 to amplify the difference between the commanded current value and actual current value, a power for supply to the IM, an induction motor (IM) 109, a three-phase power source 110, a speed detector 111, a differentiator 112, constant setters 113, 114, 115 and 116, a divider 117, an vector generator 118 to determine a speed of rotating field to be given to the IM, and an adder 119. An output of the amplifier 101 represents the torque of the IM.
With such arrangement, it is possible to control the torque (which represents a rotating force of the IM) according to the change of momentary current which varies moment by moment, based on the well-known vector controller.
Even with a slip-frequency type vector controller 100 having the basic concept shown in FIG. 11, if it is used as it is as a servo motor, an excessively abrupt acceleration/deceleration occurs so that an overslip will occur in the IM. Also even with increased primary current through the IM, a stalled condition may occur in which the torque does not increase.